Cassini's Extended Mission, July 2008 to June 2010 Options

[ynyralmaen]

I can only agree absolutely with your sentiments, but ...

As a Brit who makes no direct financial contribution to the mission,

... you may be glad to hear that your tax pounds are supporting UK operations and science on the MAG and CAPS instrument teams, and science on ISS, CDA, and CIRS! (without listing the UK involvement in Huygens!)

[nprev]

Well, as a US taxpayer, I couldn't be more proud. If given the option, I'd've given NASA the whole sum. Thanks to the Cassini team for all you do!!!

[jasedm]

The Cassini-Huygens website has posted a recent item whereby the general public can e-mail comments to the webmasters regarding the prime Mission, and the upcoming Equinox (Extended) mission. They are welcoming comments specifically regarding the website, so if anybody here has any comments, now's your chance...

See 'Your opportunity to be heard' here

[jasedm]

Looks like the mission planners have decided on the end-of-mission fate for Cassini:
Execute a sharp, banking turn at half light-speed, and plunge into Saturn's cloud tops
This from the latest Cassie 3d tool...

Attached thumbnail(s)

 

[nprev]

Unacceptable! If Cassini has enough fuel to hit 0.5c, then she'd better get X exp N Ms instead!!!

[peter59]

We have before us several months devoted almost exclusively to study Titan. Does anybody know how many and which flybys will be dedicated for radar imaging ?

[remcook]

Almost exclusively to Titan is a huge exaggeration. There's lots of other stuff going on including all these Enceladus flybys you've been seeing and studies of the rings and Saturn's atmosphere for instance. Equinox will be an interesting time for these things.
From a slide I've seen there are 13 flybys in the XM that use RADAR. Not sure what mode it will be in though for each of those, so don't know which ones are SAR.

[stevesliva]

Brief note about extended extended mission planning:

Tuesday, Nov. 11 (DOY 316):

At the Mission Planning Forum today, members of the Spacecraft Operations Office gave a presentation on power management for the post extended mission time frame. Example operational modes were presented using current instrument power allocations. Times of future power shortages were identified where the Radioisotope Thermoelectric Generator heat production decay with time will result in insufficient power being available to support all of these modes. Proposals were presented to mitigate the shortfall as needed.

[jasedm]

Hmmm interesting Steve...
I wonder what the proposals were to "mitigate the shortfall" of available power?

I know very little about the power requirements for instruments on board, so am guessing here, but what can you not do without?

Thrusters/reaction wheels, computers, communications and heaters

I suppose it must come down to a decision over which science instruments are considered 'most important' and which draw the most power - a very difficult call, which will change on each orbit according to target importance/flyby distance.

I'm guessing that fields and particles experiments don't draw a lot of power, so perhaps mission planners may consider doing without the WAC, MIMI or UVIS for interesting encounters in a putative XXM?

Incidentally, I suppose that XXM planning is now at a fairly advanced stage, as we're a little over a year and a half from the end of the XM

[jasedm]

As an addition to XXM musings, I notice that it has been at least posited that Cassini could continue actively gathering science at Saturn until the Northern summer solstice in 2017 (see Carolyn Porco's comments in 'Sector 6' on the Ciclops website here )
She points out that this would be nearly half a Saturnian year since orbit insertion.

Budgetary considerations aside, I was under the impression that propellant usage would allow another year or two at most of science operations after the extended mission finishes in 2010.

Obviously science activities would be severely curtailed with respect to the prime and extended missions, but non-targeted encounters would presumably still come about on occasion, with perhaps a handful of choice very close targeted flybys possible (Rings/Enceladus?) before EOM.

Many many 'if's' and not a few 'but's', but here's hoping.....

[elakdawalla]

I've been told that the prime mission was a bit propellant hungry because they wanted to cram so many things in to the first four years. The extended mission is a little less propellant hungry, but still has lots of targeted flybys. If they're willing to wait a long time between targeted flybys, emphasize long-term monitoring of atmosphere, rings, and magnetosphere over icy sats -- and it'd help if they could plan for a many year chunk of XXM rather than just two years at a time -- they could be quite conservative with propellant, make it last a long time.

--Emily

[tedstryk]

I've been told that the prime mission was a bit propellant hungry because they wanted to cram so many things in to the first four years. The extended mission is a little less propellant hungry, but still has lots of targeted flybys. If they're willing to wait a long time between targeted flybys, emphasize long-term monitoring of atmosphere, rings, and magnetosphere over icy sats -- and it'd help if they could plan for a many year chunk of XXM rather than just two years at a time -- they could be quite conservative with propellant, make it last a long time.

--Emily

That is always a tough one. One side of me wants to be as fuel efficient as possible. However, I would hate to play it ultraconservative and then have it pull an MGS-style vanishing act.

[elakdawalla]

I imagine the arguments go a lot like the ones about Opportunity's next goal. Opportunity wouldn't be driving to Endeavour -- a goal it may never reach -- unless there was compelling science to be done on the way. The question is whether there's a stronger case to be made for more targeted flybys and a shorter extended mission, or a long "journey" of many orbits without targeted flybys. The latter will win only if the science being done on the journey is compelling enough to compete with the science that could be done with more targeted flybys.

--Emily

[ngunn]

For me the main target is long term lake and weather monitoring of Titan. That's the place where decade-scale changes can be expected and where the available instruments can study an entire active system from surface to exosphere evolving through the seasons. Many close flybys may not be necessary for this, though a few well-spaced ones would be nice, especially for rotation studies.

[jasedm]

I suppose most people fall into two camps:

1) Keep a sentinel out at Saturn that is serviceable and able to return data for as long as possible (though at a much less intense pace than the earlier segments of the mission), observing seasonal changes and with occasional Titan flybys to constrain atmospheric properties for future missions, or further Enceladus study.

Cons:
Possible failure of the spacecraft in the longer term before all goals are achieved
Greater cost

Pros:
More numerous non-targeted flybys of other places of interest
Seasonal changes on Saturn and Titan may produce some surprises.
The unknown - What price some images of a Schumacher-Levy type event impacting the rings or atmosphere in the longer timescale?

2) Design a spectacular and daring final two-year segment to the mission

Cons:
Missing out on seasonal changes
When she's gone, she's gone

Pros:
Cheaper

The ability to conduct some seat-of-the-pants investigations with a spacecraft that is already paid-for, and which you won't get the opportunity to do again.
This might include a highly-inclined trajectory with periapsis interior to the D ring (as has been suggested) with very close study of magnetosphere, Saturn's upper atmosphere and rings.
Or remain close to the plane of the rings and skim a few kilometres above them in the final couple of orbits, perhaps with the possibility of fields and particles instruments directly sampling the 'spoke' material and ISS obtaining some very high-resolution images of the ring constituents themselves.

Perhaps we should institute a UMSF poll.....